1. Field of the Invention
This invention relates to a radiation-sensitive resin composition, and more particularly to a radiation-sensitive resin composition suitable for forming a positive type photoresist layer on a substrate having a high reflectance.
2. Description of the Prior Art
In the production of integrated circuits of high integration degrees, there have been used positive type photoresists comprising a quinone diazide compound and a novolak resin. When the positive type photoresists are applied to substrates having a high reflectance, for instance, substrates of aluminum, an aluminum alloy such as aluminum-silicon, aluminum-silicon-copper, etc., or of polysilicon, halation would occur upon irradiation with radiations. That is, upon irradiation with radiations, the light is reflected to the areas which are not to be irradiated and, as a result, it is impossible to reproduce accurately a fine photoresist pattern. In order to overcome this problem, there has been used a method of adding a radiation-absorbing material to the positive type photoresist so as to reduce the radiation transmittance of the photoresist, thereby suppressing the reflection of the radiations on the substrate at the time of irradiation.
Such an approach, however, would lead to the following problems. At the time of prebaking, which is carried out after application of the positive type photoresist to the substrate for the purpose of removing the residual solvent and thereby enhancing the adhesion between the positive type photoresist and the substrate, part of the radiation-absorbing material is sublimed from the inside of the photoresist film. The sublimation of the radiation-absorbing material may cause a considerable lowering in the antihalation effect, or may worsen the preservation stability of the positive type photoresist. Consequently, the performance of the photoresist may vary with time, or the developing property of the photoresist may be lowered, resulting in a lower resolution.